Science News - February 12, 2011

that have nothing to do with the electric dipole moment.… If you accidentally apply a small magnetic field that changes along with the electric field, it can really be a dangerous type of error.”

The way forward

Yet another group is taking a fresh approach to molecules: stripping off one electron so that the molecule has a positive charge. Because they are electrically charged, such molecular ions can be easily confined and studied.

Eric Cornell, a Nobel-winning physicist at JILA in Boulder, Colo., started the molecular ion trend seven years ago, when he wondered how he could design an experiment from scratch to detect the electron electric dipole moment. He walked down the hall and took the elevators to the office of JILA theorist John Bohn. Handing Bohn a thick stack of manila folders, one per candidate molecule, Cornell asked him to calculate which molecular ion had the best chance of being studied for an electron electric dipole moment.

centre for cold Matter/iMperial college london, www3.iMperial.ac.uK/ccM, adapted by t. dubÉ

Several detailed papers later, Bohn had a list of candidates. All of them had the peculiar property of having electrons in what’s called a “triplet delta” state. That property makes the dipole moment easier to measure because when scientists apply the electric field, they can also simultaneously measure any magnetic field that might result — the very sorts of fields that can trip up the measurements. “There’s sort of a built-in way in the molecule to monitor what the magnetic field is doing,” says Aaron Leanhardt, a former postdoc in Cornell’s lab who now works at the University of Michigan in Ann Arbor.

Cornell is now starting to build an
experiment to measure one of the ions,
known as hafnium fluoride plus, in this
triplet delta state. But so little is known
about these molecular ions that his team
must first do basic studies on the ions’
physical properties. “We’re mapping out
this terra incognita,” Cornell says. Once
he gets to measuring the dipole moment,
he says, “I think I can do it better.”
Some scientists can’t be bothered fuss-
ing with individual atoms and molecules,

Beyond the standard though the electron’s electric dipole moment, or edM, hasn’t been detected, experiments keep lowering the bar on how big it could be. reducing that limit can rule out theories that go beyond physics’ standard model. in further experiments, scientists hope to reject some leading ideas. source: iMperial college london

10–22

Electron EDM predictions for some standard model extensions

10–24

Charge × centimeters

10–26

10–34 12

10–28

10–30

10–32

3

Current limit

4

Future limit

10–36 Standard model

1. the multi-Higgs model calls for multiple types of the higgs particle, the as-yet-undiscovered particle thought to imbue others with mass.

2. in left-right symmetric models, particles behave the same way even if their direction of spin (or other qualities that are left-right dependent) is reversed.

3. the minimal supersymmetric standard model, or MSSM, is a standard model extension that holds that every elementary particle has a “superpartner.” one of the simplest versions has been ruled out by the current limit.

4. another version of MSSM that sets a parameter dubbed phi to a different value is still a possibility, but it too may be ruled out when researchers lower the bar further.

and instead are trying big chunks of solids. Such materials contain untold numbers of electrons to measure; the idea is to apply an electric field that would line up a fraction of the electron spins in the same direction as the electric field. The researchers try to detect the resulting magnetization — which in this case is not a problem, but the actual signal they are trying to measure.

At Yale, physicists Steve Lamoreaux
and Alex Sushkov think they can succeed
with ceramic materials whose electron
spins naturally align, a property that
enhances the effect of an applied electric
field. The researchers apply high voltage
to a sample of material, about the size of
a quarter, sitting in liquid helium. Using
a supersensitive magnetometer, they
detect magnetization in the ceramic as
the electric field reverses. “We study all
the physical effects going on in the sam-
ple to make sure that what we detect is
from the EDM rather than something
else,” Sushkov says.